The present invention relates to the actuator retract systems in hard disk drives and more particularly to the actuator retract systems in hard disk drives with dual mode spindle motor control.
Portable computing devices, particularly notebook computers, are gaining popularity in recent years due to their compact size, weight, and mobility. Notebook computers can operate either from AC power or from battery power. However, unlike AC power, battery power will get depleted as the notebook is being operated. The hard disk drive (HDD) is one of the devices in a notebook that uses large amounts of power when in operation. Therefore, the spindle motors in hard disk drives are intentionally operated at low speeds, measured in revolutions per minute (RPM), to minimize power consumption during battery operation. The trade-off for this lower power consumption is a decrease in RPM of the spindle motor which directly leads to a decreased performance in data access time.
When AC power is in use, power consumption is less of a concern as AC power is practically unlimited. High performance becomes more important in a hard disk drive than low power consumption. In this situation, it is desirable to have the spindle motor in the hard disk drive spin at a significantly higher RPM to allow faster data retrieval.
Virtually all hard disk drives use an actuator retract system to park the actuator in a particular position when the spindle is stopped. In contact-start-stop (CSS) drives, the actuator is parked at the ID of the disk to minimize spindle starting torque for subsequent spin-ups, and to confine head-disk contact during start-stop to a dedicated start-stop zone. In load-unload (L/UL) drives, the actuator is parked with the heads on a ramp (off the disk) to eliminate head-disk contact due to start-stop. In both cases, it is essential that the actuator is always in the proper park position when the spindle is stopped; otherwise the drive may not start reliably on subsequent spin-ups. Furthermore, in the event of sudden removal of power from the hard disk drive, the retract system must successfully park the actuator without use of external power to the drive. The system which retracts the heads in the event of loss of power is referred to as the xe2x80x9cpower-off retract systemxe2x80x9d.
Power-off retract systems generally rely on extraction of energy from the rotating spindle to provide torque to park the actuator in the absence of external power. Electrical current is derived by rectifying the 3-phase AC voltage produced by the back-emf of the rotating spindle, which functions as a generator while it coasts to a stop. Among the prior art for power-off retract systems are single phase diode rectifiers, which are often used with CSS drives because of their relatively low retract current requirements, and full-wave diode, bipolar transistor, or FET rectifiers for L/UL drives, which require more retract torque and current to park the heads on the ramp structure. Examples of bipolar transistor power-off retract circuits are described in U.S. Pat. No. 5,486,957. FET rectifiers are active rectifiers, which have potentially the highest efficiency, but are significantly more complex.
Although dual speed drives are not yet on the market, they represent an attractive option for future 2.5xe2x80x3 hard disk drives in laptop computers. Since laptops are increasingly being used in desktop and other AC-powered environments, in addition to portable battery-powered environments, provision for high performance when on AC power is becoming more important. Furthermore, the recent trend toward providing power in airplanes seats means that laptops will see more and more use in powered conditions, and less on batteries.
Power-off retract systems for dual speed drives have unique requirements, since the drive may be running in either mode (high or low RPM) at the moment of power off. In both cases, the applied retract torque should be approximately the same. Retract systems are designed to provide a specific current to the actuator; this current must be high enough to successfully park the actuator under all expected conditions (temperature, humidity, age, etc. and for the full range of manufacturing tolerances (torque constant of spindle and actuator, resistance of spindle and actuator, ramp friction, flex cable tension, etc. but no higherxe2x80x94too much retract current results in excessive shock to the fragile head-gimbal assemblies as they climb the L/UL ramp and the actuator impacts its crash stop. Therefore, the power-off retract system should be regulated to provide a fixed output regardless of input, or switched to take into account which RPM the spindle is running at the moment of power-off.
A need therefore exists for providing a power-off retract system that provides the desired retract current for both low and high RPM conditions at the moment of power-off.
A principle objective of the present invention is to provide a power-off retract system that provides the desired retract current for both low and high RPM conditions at the moment of power-off.
In one embodiment, the resistance of one part of the retract circuit is controlled to control the back-emf current flowing into a voice coil motor. A signal from the Main Processor Unit controls the increase or decrease in the resistance of the circuit.
In another embodiment, the circuit utilizes the 3 phases of the motor windings. The spindle motor generates back-emf from the 3 windings and therefore the back-emf is generated in 3 phases. The circuit can selectively restrict which winding is allowed to supply back-emf current to the voice coil motor. In the 1-phase configuration, only one of the spindle motor windings is supplying back-emf current to the voice coil motor and therefore the retract power is the weakest in this configuration. In the 3-phase configuration, all three windings are supplying back-emf current to the voice coil motor and therefore the retract power is the strongest in this configuration. The 1-phase configuration is used in the high speed mode when the back-emf generated by the spindle motor is the highest. The 3-phase configuration is used in the low speed mode when the back-emf generated by the spindle motor is the smallest.
In yet another embodiment, a voltage or a current regulator is used to control the current flowing into the voice coil motor. In the voltage regulator, an operational amplifier is used to compare the voltage from the rectifier circuit to a reference voltage. A transistor is used to stopped the current from flowing into the voice coil motor if the voltage from the rectifier circuit is larger than the reference voltage.